topic Re: nsswitch question in Operating System - Linux

nsswitch question

Lynn Hsu_2 — Thu, 13 Jul 2006 13:03:14 GMT

Hi,
I have a Redhat webserver (HP DL360). When
doing "nslookup hostA" it said not found even
hostA is in /etc/hosts. The nsswitch.conf
defines to search files first:
hosts: files [NOTFOUND=continue] dns

The /etc/resovle.conf looks like this:
domain xyz.com
search xyz.com
nameserver 192.168.xx.yy

Why nslookup did not go to files first? what's wrong with nsswitch.conf file?

Lynn

Re: nsswitch question

Ivan Ferreira — Thu, 13 Jul 2006 15:12:02 GMT

The nslookup dig and host command will always try to use only DNS, they won't consult the /etc/hosts file. There is nothing wrong with your nsswitch.conf file.

Re: nsswitch question

TwoProc — Thu, 13 Jul 2006 16:37:58 GMT

The command to resolve a name to an ip address - regardless of whether or not it is resolved in a dns server, or a host file, nis etc. is already in linux.

Run "gethostip" from the command line.

$> gethostip hostA

will return something like
hostA 192.168.xxx.xxx [8 digit hex number]

so, you'd want something like

$> gethostip hostA | cut -f 2 -d" "
192.168.xxx.xxx

Re: nsswitch question

TwoProc — Thu, 13 Jul 2006 16:43:43 GMT

This "may" end up looking like a repost.
Sorry if it does, it is taking about FIVE minutes to post right now, and I saw a change I wanted to make, and instead of a follow up - I'm trying to get it all in one post, in case it hasn't gone through yet.
--------Excuse if it is a double post--------

The command to resolve a name to an ip address - regardless of whether or not it is resolved in a dns server, or a host file, nis etc. is already in linux.

Run "gethostip" from the command line.

$> gethostip hostA

will return something like
hostA 192.168.xxx.xxx [8 digit hex number]

$> gethostip -d hostA

will return just the ip address

HTH

Re: nsswitch question

Lynn Hsu_2 — Thu, 13 Jul 2006 16:46:28 GMT

Thanks for the replies. So on Linux, is nsswitch.conf still useful? I think
it is for the name resolution search order.

Lynn

Re: nsswitch question

Steven E. Protter — Fri, 14 Jul 2006 06:35:37 GMT

Shalom,

nsswitch.conf is critical. It decides how a system will resolve hostnames, how it will authenticate users, any number of things.

It is problably the most important configuration file after the network configuration.

As posted your nsswitch.conf file, which must be in the /etc directory should look in files first and then if not found continue to DNS.

SEP

Re: nsswitch question

Mark Fenton — Fri, 14 Jul 2006 17:44:28 GMT

The issue you are seeing is that nslookup doesn't use nsswitch.conf to determine where to find conversions from names to numbers, just resolv.conf.

applications like 'ping' use the standard system calls to do their resolution work.

Re: nsswitch question

TwoProc — Fri, 14 Jul 2006 17:52:16 GMT

That's right Lynn.
It is for name resolution search order (among other things).

U got it.

Re: nsswitch question

Lynn Hsu_2 — Wed, 19 Jul 2006 13:33:53 GMT

Thanks everyone.

Lynn

Re: nsswitch question

Lynn Hsu_2 — Wed, 19 Jul 2006 13:35:30 GMT

Got the answer.